November
15, 2004: Where the rain forests of Guatemala now stand, a great
civilization once flourished. The people of Mayan society built vast
cities, ornate temples, and towering pyramids. At its peak around
900 A.D., the population numbered 500 people per square mile in rural
areas, and more than 2,000 people per square mile in the cities --
comparable to modern Los Angeles County.

This
vibrant "Classic Period" of Mayan civilization thrived for
six centuries. Then, for some reason, it collapsed.

Right:
Mayan ruins in Guatemala. Photo copyright Tom Sever.

The fall of the Maya has long been one of the great mysteries of
the ancient world. But it's more than a historical curiosity. Within
sight of the Mayan ruins, in the Petén region of Guatemala near
the border with Mexico, the population is growing again, and rain forest
is being cut to make farmland.

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"By learning what the Maya did right and what they did wrong,
maybe we can help local people find sustainable ways to farm the land
while stopping short of the excesses that doomed the Maya," says
Tom Sever at the Marshall Space Flight Center (MSFC).

Sever, NASA's only archeologist, has been using satellites to examine
Mayan ruins. Combining those data with conventional down-in-the-dirt
archeological findings, Sever and others have managed to piece together
much of what happened:

From pollen trapped in ancient layers of lake sediment, scientists
have learned that around 1,200 years ago, just before the civilization's
collapse, tree pollen disappeared almost completely and was replaced
by the pollen of weeds. In other words, the region became almost completely
deforested.

Without
trees, erosion would have worsened, carrying away fertile topsoil.
The changing groundcover would have boosted the temperature of the
region by as much as 6 degrees, according to computer simulations
by NASA climate scientist Bob Oglesby, a colleague of Sever at the
MSFC. Those warmer temperatures would have dried out the land, making
it even less suitable for raising crops.

Rising temperatures would have also disrupted rainfall patterns,
says Oglesby. During the dry season in the Petén, water is
scarce, and the groundwater is too deep (500+ feet) to tap with wells.
Dying of thirst is a real threat. The Maya must have relied on rainwater
saved in reservoirs to survive, so a disruption in rainfall could
have had terrible consequences.

(Changes in cloud formation and rainfall are occurring over deforested
parts of Central America today, studies show. Is history repeating
itself?)

Using classic archeology techniques, researchers find that human
bones from the last decades before the civilization's collapse show
signs of severe malnutrition.

"Archeologists
used to argue about whether the downfall of the Maya was due to drought
or warfare or disease, or a number of other possibilities such as
political instability," Sever says. "Now we think that all
these things played a role, but that they were only symptoms. The
root cause was a chronic food and water shortage, due to some combination
of natural drought and deforestation by humans."

Today, the rain forest is again falling under the axe. About half
of the original forest has been destroyed in the last 40 years, cut
down by farmers practicing "slash and burn" agriculture:
a section of forest is cut down and burned to expose soil for planting
crops. It's the ash that gives the soil its fertility, so within 3-5
years the soil becomes exhausted, forcing the farmer to move on and
cut down a new section. This cycle repeats endlessly ... or until
the forest is gone. By 2020, only 2% to 16% of the original rain forest
will remain if current rates of destruction continue.

It seems that modern people are repeating some of the Maya's mistakes.
But Sever thinks disaster can be averted if researchers can figure
out what the Mayans did right. How did they thrive for so many centuries?
An important clue comes from space:

Sever and co-worker Dan Irwin have been looking at satellite photos
and, in them, Sever spotted signs of ancient drainage and irrigation
canals in swamp-like areas near the Mayan ruins. Today's residents
make little use of these low-lying swamps (which they call "bajos,"
the Spanish word for "lowlands"), and archeologists had
long assumed that the Maya hadn't used them either. During the rainy
season from June to December, the bajos are too muddy, and
in the dry season they're parched. Neither condition is good for farming.

Sever suspects that these ancient canals were part of a system devised
by the Maya to manage water in the bajos so that they could
farm this land. The bajos make up 40% of the landscape; tapping
into this vast land area for agriculture would have given the Maya
a much larger and more stable food supply. They could have farmed
the highlands during the wet season and the low-lying bajos
during the dry season. And they could have farmed the bajos
year after year, instead of slashing and burning new sections of rain
forest.

Could today's Petén farmers take a lesson from the Maya and
sow their seeds in the bajos?

It's an intriguing idea. Sever and his colleagues are exploring that
possibility with the Guatemalan Ministry of Agriculture. They're working
with Pat Culbert of the University of Arizona and Vilma Fialko of
Guatemala's Instituto de Antropología e Historia to identify
areas in the bajos with suitable soil. And they're considering
planting test crops of corn in those areas, with irrigation and drainage
canals inspired by the Maya.

A message from 900 A.D.: it's never too late to learn from your ancestors.